1. Field of the Invention
This invention relates to a method for recycling expanded polymers, particularly expanded thermoplastic polymers, more particularly expanded polystyrene polymers.
2. Discussion of Related Art
Expanded synthetic polymeric resins are widely utilized for fabricating packaging and packing products, as well as numerous other uses such as building materials, etc. When objects and materials contained in packaging and packing products are utilized, the packaging and packing products are discarded. If these products are merely disposed in landfills, they are lost for subsequent recovery of the constituent material. Furthermore, disposal in landfills is objectionable since such products, as is typical with synthetic resins generally, are of low density and occupy inordinate volume within a landfill.
It is thus desirable to recover the expanded materials in a form rendering the material suitable for reuse into other products, including being reformed into additional packaging. Several recycling methods of these expanded materials have been developed.
U.S. Pat. No. 5,935,536 describes an apparatus and method for reclaiming expanded synthetic resin wastes in a form suitable for subsequent injection molding. The apparatus includes a tank containing a solvent having a pump for pumping dissolved resin wastes to an evaporator. The evaporator comprises an endless belt on which dissolved resin waste is deposited and precipitates in the form of a thin film. A heater is disposed below the belt to expedite separation of solute and solvent by evaporation. A blower disposed within a housing enclosing the endless belt establishes air circulation over the belt, further promoting evaporation. The thin film is wound on a roller and subjected to a heated roller to fuse the many thin film strata into a solid, generally cylindrical mass. The solid mass is then comminuted by a granulator. Evaporated solvent is recovered in a condenser and is reused.
U.S. Pat. No. 5,629,352 describes a solvent for polystyrene having an excellent dissolving ability and chemical stability. A relatively simple recycling or reutilizing process of both the polystyrene foam and the solvent is also disclosed. The solvent comprises at least one member selected from the group consisting of such a glycol ether compound as diethylene glycol dimethyl ether, diethylene glycol diethyl ether or dipropylene glycol dimethyl ether, and such a fatty acid dialkyl ester compound as dimethyl succinate, dimethyl glutarate or dimethyl adipate. The method comprises first dissolving the polystyrene foam in the solvent, and then (1) distilling the obtained solution at a temperature at which polystyrene does not decompose to separate the solvent from polystyrene, (2) precipitating polystyrene from the obtained solution by adding water to the solution, or (3) precipitating polystyrene from the obtained solution by cooling the solution to a temperature lower than the temperature at which polystyrene dissolves.
U.S. Pat. No. 5,462,233 describes a process for recovering recyclable expanded particles from expanded particle moldings including expanded particles of a synthetic resin coated with thermoplastic resin (interfacial material) whose melting point is lower than that of the synthetic resin of the expanded particles or whose solubility is different from that of the synthetic resin of the expanded particles. The process includes the steps of softening or melting the interfacial material by heating or dissolving it with a solvent, and separating the expanded particle molding into individual particles by applying a shearing force thereto under circumstances such that the bond strength among the expanded particles in the molding is weakened.
A common feature among the prior art procedures for recovering materials from expanded polymeric materials is the use of solvents in compacting the expanded polymer. However, the use of solvents is undesirable in many respects. First, the use of solvents in general increases the cost of the recovery operation. Second, most solvents require special handling during the process and must be disposed of as hazardous waste following use in the process. Third, the use of solvents may result in the generation of hazardous gases. Fourth, the use of solvent increases the length of the process because recovery of the material from the solvent requires additional processing steps and apparatuses as noted in the patents discussed above. This is very significant in that the existing processes are not able to handle sufficient volume to keep up with the amount of expanded polymer waste being generated. Fifth, the solvents themselves may chemically interact with the material being recovered, thereby adversely modifying the properties of the material and thus limiting the utility of the recovered material in the manufacture of recycled products.
It would thus be desirable to develop a simple and cost effective process for recovering polymer material in particle form from expanded polymer.
It is thus an object of the present invention to obtain a simple, cost-effective and speedy process for recovering polymeric particle materials from expanded polymers. It is a further object of the invention to obtain a process for recovering polystyrene from expanded polystyrene.
It is a still further object of the invention to obtain a process of recovering polymer materials from expanded polymers in a mechanical process that is free of the use of any solvents in the recovery process.
These and other objects are achieved by the present invention, which achieves a process for recovering polymer materials from expanded polymer materials by grinding/compacting the expanded polymer materials in the presence of hot air and ionized air. The polymer of the expanded polymer is recovered in particle form, and is suitable for reuse in manufacturing recycled products. These and other objects are also achieved by the invention, which achieves an apparatus for carrying out the process of the invention.
The invention employs mechanical procedures for recovery of the polymer material, and thus avoids the use of chemical procedures, i.e., the use of solvents, and the problems associated therewith as discussed above.